The Pentagon 's most expensive weapons program ever , the F-35 warplane , is cleared for takeoff again .

The limited flight clearance , approved by Navy and Air Force officials Monday , allows the aircraft to fly with an engine inspection regimen and restricted flight envelope following the fleet 's grounding after an engine fire last month .

Defense Department spokesman Mark Wright said in a statement Tuesday the restrictions would `` remain in effect until the root cause of the June 23 engine mishap is identified and corrected . ''

It had been hoped that the stealth fighter would be able to make an appearance at the famed Farnborough air show , under way now , but Pentagon spokesman Rear Adm. John Kirby said Tuesday afternoon that wo n't happen .

`` The Department of Defense , in concert with our partners in the U.K. , has decided not to send Marine Corps and U.K. F-35B aircraft across the Atlantic to participate in the Farnborough air show , '' he told reporters . `` This decision was reached after a consultation with senior leaders and airworthiness authorities , despite the decision by airworthiness authorities to clear the aircraft to return to flight -- to limited flight . ''

The 2014 Farnborough International Airshow began Monday , and runs through July 20 in Farnborough , England . The opening day brought $ 42 billion of orders and commitments for commercial aircraft and engines , according to a statement from the show 's organizers .

The F-35 was developed at a cost of nearly $ 400 billion so far and beset for years by cost overruns and delays . The so-called Joint Strike Fighter was temporarily grounded following a fire on the runway at Eglin Air Force Base in Florida . No one was hurt .

Engine maker Pratt & Whitney worked with Air Force investigators to inspect all engines in the fleet .

`` We have great confidence in the F135 engine powering the F-35 , and we have worked very closely with DoD and the Services to return the aircraft to flying status , '' Matthew Bates , communications manager for Pratt & Whitney Military Engines , said in a statement Tuesday .

The F-35 's lead contractor , Lockheed Martin , which is producing variants of the plane for the U.S. Navy , Marines and Air Force , also worked with investigators following the fleet 's grounding .

F-35 future

The Pentagon wants more than 2,400 of the fighter jets ultimately , while hundreds more are expected over time to go to allies such as South Korea , Japan and Australia .

More than 100 planes have been built so far , most for testing , but the program is still in its development and training phases .

The military says the stealthy fighter will be `` the most affordable , lethal , supportable and survivable aircraft ever to be used '' by so many services worldwide .

But its production has been controversial for its soaring cost history -- the price tag has nearly doubled from early estimates , to $ 135 million per unit as of last year , according to a U.S. Government Accountability Office report in March -- as well as its schedule , software and other setbacks . Test flights began in 2007 .

While all models have been grounded in the past for various problems , the version for the Marines , the F-35B , has had more issues . Experts say that 's mainly due to its design for shorter takeoffs and vertical landings .

Richard Aboulafia , a Teal Group analyst , said earlier this month that every component of the F-35 overall `` is pushing the frontiers of technology '' as engineers combine extraordinary engine power with a lighter weight design .

He said the program has made gradual progress in recent years where glitches get resolved pretty quickly compared with 18 to 24 months ago , when setbacks seemed to come one right after another .

`` It 's a tremendously complex project , '' he said , adding that cost issues remain a concern .

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The F-35 wo n't participate in the Farnborough air show , Pentagon spokesman says

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The return to flight order is a limited flight clearance

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The F-35 fleet was grounded after an engine fire in June

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Pratt & Whitney , Lockheed Martin working with investigators to find cause of fire